Encapsulant material for solar cell module and laminated glass applications

ABSTRACT

An encapsulant material includes a layer of metallocene polyethylene disposed between two layers of an acid copolymer of polyethylene. More specifically, the layer of metallocene polyethylene is disposed adjacent a rear surface of the first layer of the acid copolymer of polyethylene, and a second layer of the acid copolymer of polyethlene is disposed adjacent a rear surface of the layer of metallocene polyethylene. The encapsulant material can be used in solar cell module and laminated glass applications.

This is a continuation-in-part application of U.S. patent applicationSer. No. 08/899,512 filed on Jul. 24, 1997 pending.

GOVERNMENT INTEREST

The subject matter described herein was supported in part byPhotovoltaic Manufacturing Technology (PVMaT) Contract No.ZAP-5-14271-09.

FIELD OF THE INVENTION

The invention relates to encapsulant materials for various applications.More particularly, the invention relates to an encapsulant material forsolar cell module and laminated glass applications.

BACKGROUND

Transparent encapsulant materials are used in numerous applications,including solar cell module and laminated glass applications. In solarcell applications, transparent encapsulants protect and seal theunderlying solar cells without adversely affecting the opticalproperties of such underlying materials. In laminated glassapplications, transparent encapsulants minimize any possible hazardsfrom broken glass. In these applications, the encapsulant is exposed tothe ultraviolet (UV) rays of the sun and this exposure can result in theyellowing and physical degradation of the polymer. To prevent this, UVstabilizers are added to the encapsulant.

In the manufacture of crystalline silicon solar cell modules, atransparent encapsulant material is used to protect the brittle siliconsolar cells from breakage and to help seal these cells into the overallmodule structure. The encapsulant material is usually a thermoplastic.The thermoplastic is melted, then flows to fill in any open spaces inthe module and bonds to all adjacent surfaces. The most widely usedencapsulant material for solar cell modules is a copolymer of vinylacetate and ethylene, known as ethylene vinyl acetate (EVA). EVA is usedto encapsulate and seal both thin film and crystalline silicon solarcell modules.

There are several disadvantages associated with using EVA as anencapsulant material that adversely affect the quality and manufacturingcost of the solar cell modules. First, an organic peroxide is added toEVA in order to cross-link it using the heat which accompanies thelamination process. The cross-linking is necessary to increase the creepresistance of the encapsulated structure. However, the peroxide is notcompletely consumed during the cross-linking process, and the remainingperoxide can promote subsequent oxidation and degradation of EVA. Inaddition, the EVA must be laminated in a vacuum when making a modulebecause of the presence of peroxide in the EVA. The reason for this isthat oxygen lowers the degree of cross-linking, producing anunsatisfactory encapsulant. Second, the preferred EVA usually contains33% (by weight) of vinyl acetate, and thus is a very soft and tackysubstance that tends to stick to itself. This tackiness makes handlingof the EVA material in a manufacturing environment much more troublesomeand also makes it more expensive to manufacture the base resin. As such,the EVA material requires a release paper or liner material to use thematerial after it has been made into sheet. Third, peroxide cured EVAhas been known to turn yellow and brown under extensive exposure tosunlight for several years. Yellowing and browning causes reduction insolar module power output. Fourth, EVA can produce acetic acid underprocessing conditions which can then foster metal contact corrosion.Fifth, EVA is known to be fairly permeable to water and is, therefore,far from ideal as a sealant.

Although virtually any transparent polymer eventually shows somedegradation and yellowing after exposure to sunlight, an encapsulantmaterial that can withstand degradation and yellowing for a longerperiod of time than EVA is desirable. Ideally, a solar cell moduleshould last for thirty years without showing much sign of degradation.EVA is unlikely to satisfy this thirty year duration requirement. Inaddition to finding a suitable replacement for EVA (or PVB, which isdescribed below), it is also necessary to develop a suitable UV lightstabilization package for the encapsulant.

In laminated glass applications, the laminated glass is made by forminga sandwich of two pieces of glass with a sheet of a transparent polymerdisposed between the two pieces. This transparent polymer sheet servesto prevent the glass in the laminated structure from shattering intodangerous shards when the glass is broken. Windshields on automobilesand architectural glass are manufactured in this manner. Poly vinylbutyral (PVB) is a widely used material in such polymer sheets in theforegoing laminated glass applications. PVB, however, has severaldrawbacks. First, PVB is extremely hydroscopic (i.e. it absorbs moisturereadily). Therefore, it must be kept refrigerated and maintained underspecial atmospheric conditions before it can be successfully laminated.Second, PVB is also extremely soft and tacky and, therefore, must beused with a release or liner layers.

SUMMARY OF THE INVENTION

This invention features an encapsulant material that may be used insolar cell modules, laminated glass and a variety of other applications.The encapsulant material is a three layer structure. A middle layer isformed of metallocene polyethylene and disposed between two outer layersof an acid copolymer of polyethylene. The layer of metallocenepolyethylene can comprise copolymers of ethylene with butene, hexene, oroctene.

The acid copolymer layers can be derived from any direct or graftedethylene copolymer of an alpha olefin having the formula R—CH═CH₂, whereR is a radical selected from the class consisting of hydrogen and alkylradicals having from 1 to 8 carbon atoms and alpha, beta-ethylenicallyunsaturated carboxylic acid having from 3 to 8 carbon atoms. The acidmoieties are randomly or non randomly distributed in the polymer chain.The alpha olefin content of the copolymer can range from 50-92% whilethe unsaturated carboxylic acid content of the copolymer can range fromabout 2 to 25 mole percent, based on the alpha olefin-acid copolymer.

The layers of metallocene polyethylene and acid copolymer areexceptionally transparent. In one detailed embodiment, the metallocenepolyethylene layer is formed from a copolymer of ethylene and octene,and the acid copolymer layers are based on an ethylene methacrylic acidcopolymer.

An encapsulant material which is a combination of these two materialsallows for the exploitation of the best properties of each materialwhile overcoming the limitations of either EVA or of each material ifused alone. The outer acid copolymer layers allow the encapsulantmaterial to bond strongly to all the adjacent surfaces (e.g. a backskinformed of any suitable material). The inner metallocene polyethylenelayer which forms the bulk of the encapsulant material is a highlytransparent, low cost thermoplastic material. The two acid copolymerlayers are thin (i.e., the order of 0.001-0.004″ thick), and may bebased on either an ethylene methacrylic acid copolymer or ethyleneacrylic acid copolymer (such copolymers containing 7-15% by weight ofthe carboxylic acid). This level of acid content promotes strongadhesive bonds with the glass superstrate, the silicon cells, and therear backing surface of the encapsulated system as well as exhibitinghigh light transmission. The metallocene polyethylene has excellentoptical clarity and superior physical properties compared to the acidcopolymers. These superior properties are derived from the fact that themetallocene catalyst used results in a polymer with narrow molecularweight distribution.

There are several advantages associated with an encapsulant materialwhich is a combination of the metallocene polyethylene and the acidcopolymer materials. One of these advantages involves the bondingstrength of the encapsulant with all adjacent surfaces. The bondingstrength is qualitatively described by the method in which the bondfailure occurs under test conditions. Adhesive bond failure describesthe case in which the bond at the interface fails. Cohesive failuredescribes a much stronger bond, whereby the polymer material itselffails before the interface bond. In this case, the interface bond isstronger than the internal bonding of the polymer (i.e., theencapsulant) itself. Because of their acid functionality, the outer acidcopolymer layers will result in cohesive bond failure. The metallocenepolyethylene, on the other hand, will only result in adhesive bondfailure, as will EVA.

Also, because of its tight molecular weight distribution, metallocenepolyethylene, used alone, would have a rather narrow melting rangemaking the fabrication of sheet from this material problematic andcreating difficulties in lamination.

Alternatively, the encapsulant material may be a combination of themetallocene polyethylene as the inner layer and ionomers as the twoouter layers. Ionomers may be fabricated by neutralizing the acidcopolymers with metal ions from any of the Group I, II or III typemetals.

In contrast to EVA and PVB, the encapsulant material of the presentinvention is not tacky and can be easily handled in a manufacturingenvironment without the need for any release paper. Furthermore, acidcopolymers are totally insensitive to moisture and the finished sheet ofencapsulant material does not need special storage, as required for, anddoes not need to be kept in sealed dark bags as required for EVA.

The invention also features a solar cell module including theabove-described encapsulant material. The module comprises at least onesolar cell and the encapsulant material disposed adjacent to at leastone surface of the solar cell. A front support layer is formed of thelight transmitting material disposed adjacent a front surface of theencapsulant material, and a backskin layer disposed adjacent a rearsurface of the encapsulant material. The front support layer andbackskin layer are laminated to encapsulate and seal the solar cell fromthe ambient atmosphere.

The invention also features a laminated transparent member including theabove-described encapsulant material. The member comprises a frontsupport layer formed of transparent material, the transparentencapsulant layer and a rear support layer formed of transparentmaterial. The transparent encapsulant layer is disposed adjacent a rearsurface of the front support layer. The rear support layer is disposedadjacent a rear surface of the encapsulant layer. The front and rearsupport layers can be glass or plastic.

The invention also features a method of manufacturing an encapsulantmaterial. The method includes the steps of: providing a sheet ofmetallocene polyethylene; placing a first layer of acid copolymeradjacent a front surface of the sheet of metallocene polyethylene; andplacing a second layer of acid copolymer adjacent a rear surface of thesheet of metallocene polyethylene. The layers of acid copolymer can bebonded to the front and rear surfaces of the sheet of metallocenepolyethylene. In one detailed embodiment, a three ply sheet ofencapsulant material can be produced from any of several processes forcoextrusion of thermoplastics. Alternatively, the acid copolymer in thefirst layer and the second layer may be neutralized to form the firstand second ionomer layers.

The invention also features a method of manufacturing a solar cellmodule comprising the steps of: providing at least one solar cell;forming the above-described transparent encapsolant material; placingthe encapsulant material adjacent at least one surface of the solarcell, preferably two; and positioning the solar cell and the encapsulantmaterial between a transparent front support layer and a backskin layer.

The invention also features a method of manufacturing a laminatedtransparent member comprising the steps of: providing two transparentsupport layers; forming the above-described transparent encapsulantmaterial; placing the encapsulant material between the two supportlayers to form an assembly; and laminating the assembly to encapsulatethe support layers with the encapsulant layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an encapsulant materialincorporating the principles of the invention.

FIG. 2 is a cross-sectional view of a crystalline silicon solar cellmodule encapsulated with the encapsulant material of FIG. 1.

FIG. 3 is a cross-sectional view of a solar cell module in which theencapsulant material and a backskin encapsulates the solar cells.

FIG. 4 is a cross-sectional view of a Copper Indium Diselenide thin filmsolar cell module which includes the encapsulant material.

FIG. 5 is a cross-sectional view of an amorphous silicon solar cellmodule which includes the encapsulant material.

FIG. 6 is a cross-sectional view of a Cadmium Telluride thin film solarcell module which includes the encapsulant material.

FIG. 7 is a cross-sectional view of a laminated glass structure whichincludes the encapsulant material.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of a transparent encapsulant material10 incorporating the principles of the invention. In one embodiment, theencapsulant material 10 can be used in a solar cell module to protectcrystalline silicon solar cells from breakage when they are in a moduleand subjected to mechanical stress during field usage. The encapsulantmaterial also serves to seal the module, which is particularly importantfor thin film modules. In another embodiment, the encapsulant material10 can be laminated between two pieces of glass or transparent polymerto provide a composite structure that does not shatter when broken.

The encapsulant material 10 comprises an inner layer 12 and outer layers14 and 16. The outer layer 14 is disposed adjacent a front surface 18 ofthe inner layer 12, and the outer layer 16 is disposed adjacent a rearsurface 19 of the inner layer 12. The inner layer 12 comprises a highlytransparent thermoplastic material. The outer layers 14, 16 are made oftransparent polymer material that is capable of heat bonding to variousmaterials including glass, metals and other polymers.

In one embodiment, the inner layer 12 can be formed of metallocenepolyethylene and the outer layers 14, 16 can be formed of an acidcopolymer. Metallocene polyethylene is prepared by using as a catalystan organometallic coordination compound which is obtained as acyclopentadienyl derivative of a transition metal or a metal halide. Anacid copolymer, for example, may comprise copolymers of ethylene andmethacrylic acid, or ethylene and acrylic acid.

Adding 14% comonomer of octene to the metallocene polyethylene producesan inner layer 12 having excellent optical clarity. Moreover, the innerlayer 12 has improved physical properties because the catalyst methodused to prepare the material produces a polymer with a narrow molecularweight distribution. Polymers made with the usual catalysts tend to havesignificant components of lower molecular weights. The latter reduce themechanical properties of the overall polymer, as compared with thehigher molecular weight components of the polymer. Because a polymermade from a metallocene catalyst has a tighter molecular weightdistribution and fewer lower molecular weight components, it exhibitsgreater mechanical strength and puncture resistance.

Although metallocene polyethylene has good optical properties, it formsbonds which exhibit adhesive failure instead of the much strongercohesive failure. Metallocene polyethylene is also difficult to processdue to its narrow molecular weight distribution. A thermoplasticmaterial with a narrow molecular weight distribution has a narrowmelting range, making fabrication of a sheet of the material orlamination difficult. Providing outer layers 14, 16 formed of acidcopolymer solves these problems.

In one embodiment, the outer layers 14, 16 are formed of an acidcopolymer havig a high acid content (about 9% by weight free acid). Thehigh acid content provides strong bonds (i.e., cohesive failures ondelamination testing) and improves the optical properties of the acidcopolymer. The metallocene polyethylene inner layer 12 comprisesethylene alpha-olefin with 14% comonomer of octene. This three layeredstructure displays interesting optical properties. When this encapsulantmaterial is laminated under heat and pressure, it appears cloudy andlight blue. However, when the total light transmission through thematerial is measured using an integrating sphere, it has been found thatthe total amount of light going through the material is over 90%. Thisis due to micro or nano crystalline size regions within the outer acidcopolymer layers which scatter the incident light. The result ofencapsulating a solar cell with the encapsulant of the invention is thatthere is no reduction in light reaching the cell as compared to an EVAencapsulated solar cell.

The short circuit current density which is a direct measure of theamount of light reaching the solar cell, was measured on solar cellswithout lamination and solar cells laminated with the encapsulant of theinvention and also with EVA under a piece of glass. Four samples withthe new encapsulant and four samples with cross linked EVA weremeasured, with the result that the new encapsulant samples showed a netaverage gain in short circuit current of 2.2% and the EVA samples a netaverage gain of 1.7% after lamination.

The encapsulant material 10 can be formed by any number of film or sheetcoextrusion processes, such as blown-film, modified blown-film,calendaring, and casting. In one embodiment, the encapsulant material 10is formed by coextruding, in a blown film process, the metallocenepolyethylene layer 12 and the acid copolymer layers 14, 16. Inparticular, the layer of metallocene polyethylene 12 includes first andsecond sublayers 12 a, 12 b of metallocene polyethylene. The first acidcopolymer layer 14 is coextruded with the first sublayer 12 a ofmetallocene polyethylene, and the second acid copolymer layer 16 iscoextruded with the second sublayer 12 b of metallocene polyethylene.The first layer 12 a of metallocene polyethylene (along with the firstacid copolymer layer 14) is then bonded to the second layer 12 b ofmetallocene polyethylene (along with the second acid copolymer layer 16)to produce the encapsulant material 10. In this way, a thickerencapsulant layer and the desired 3-layer structure can be formed.

The acid copolymer layers 14, 16 can have a thickness in the range of0.001-0.004 inch, and the layer 12 can be of any desired thickness. Forsolar cell applications, the layer 12 can have a thickness ofapproximately 0.015 inch such that the overall thickness of theencapsulant material 10 has a thickness of approximately 0.018 inch. Theencapsulant material 10 can be manufactured as elongated sheet that canbe stored in convenient rolls of any desired width.

Alternatively, the inner layer 12 can be formed of metallocenepolyethylene and the outer layers 14, 16 can be formed of an ionomer.The ionomer may be formed by neutralizing the acid copolymer with metalions. The process of forming an encapsulant material comprising acidcopolymers, as described above, may also be used to form the encapsulantmaterial comprising ionomers.

FIG. 2 is a cross-sectional view of a solar cell module 20 in which theencapsulant material 10 encapsulates interconnected crystalline siliconsolar cells 22. The encapsulant material 10 is disposed adjacent thefront 23 and rear surfaces 24 of the interconnected solar cells 22. Theencapsulant material 10 adjacent the rear surfaces 24 of theinterconnected solar cells 22 may be pigmented. The encapsulant material10 may be bonded to the interconnected solar cells 22. A front supportlayer 26 formed of light transmitting material covers front surfaces 23of the encapsulated interconnected solar cells 22. The front supportlayer 26 may be formed of glass or transparent polymer. A backskin layer28 is disposed adjacent to the rear surfaces 24 of the encapsulatedinterconnected solar cells 22. The backskin layer 28 can be formed of(1) a polymer such as tedlar laminate, (2) a thermoplastic material thatcan be used to form edge sealing, thus eliminating the need for analuminum frame, or (3) a piece of glass forming a double glass module.In one detailed embodiment, the backskin layer 28 can be a thermoplasticpolyolefin comprising a mixture of at least two acid copolymers such asa sodium acid copolymer and a zinc acid copolymer with or without 10-20%(by weight) glass fiber.

FIG. 3 is a cross-sectional view of a solar cell module 30 in which theencapsulant material 10 and the backskin layer 28, in combination,encapsulate the interconnected solar cells 22. The encapsulant material10 is disposed adjacent the front surfaces 23 but not the back surfacesof the interconnected solar cells 22. The encapsulant material need notbe placed adjacent the rear surfaces 24 of the interconnected solarcells 22. The backskin layer 28 serves as the rear encapsulant and asthe rear surface of the module.

FIG. 4 is a cross-sectional view of a solar cell module 40 whichincludes a thin film of Copper Indium Diselenide (CIS). A Zinc Oxide(ZnO) layer 32 is disposed on a front surface 31 of the Copper IndiumDiselenide (CIS) film 34 and a back contact 36 is disposed on a rearsurface 33 of the film 34. The encapsulant material 10 is disposed onthe ZnO layer 32 and the front support layer 26 is disposed on theencapsulant material 10. The substrate layer 28, which can be formed ofglass, plastic or metal, is disposed adjacent a rear surface of the backcontact 36. For purposes of this invention, CIS is considered equivalentto the general class of I-III-VI₂ compounds such as the pentenarycompound Cu(In,Ga)(Se,S)₂. Also, the transparent conducting layer (i.e.,the ZnO layer) is considered the equivalent to the combination of thetransparent conducting layer with a thin buffer layer (e.g., a 500 Ålayer of CdS).

FIG. 5 shows a cross-sectional view of an amorphous silicon solar cellmodule 50 comprising the encapsulant material 10. A layer of thintransparent conducting oxide 42 (e. g., Tin Oxide (SnO₂)) is coated on afront support layer 26 comprising glass. An amorphous silicon layer 44is disposed adjacent a rear surface of the oxide layer 42, and a rearcontact 46 is disposed adjacent a rear surface of the amorphous siliconlayer 44. The encapsulant material 10 is disposed adjacent a rearsurface of the rear contact 46. The backskin layer 28, which can beformed of glass, plastic or metal, is disposed adjacent a rear surfaceof the encapsulant material 10. A front support layer comprising glassis disposed on the oxide layer 42.

FIG. 6 is a cross-sectional view of a Cadmium Telluride (CdTe) thin filmmodule 60. A rear surface of the front support layer 26 is coated with athin transparent conducting oxide layer 42. A layer of Cadmium Sulfide(CdS) 52 is placed adjacent to a rear surface of the oxide layer 42, anda layer of Cadmium Telluride (CdTe) 54 is placed adjacent a rear surfaceof the CdS layer 52. A rear contact 42 is placed adjacent a rear surfaceof the CdTe layer 54. The encapsulant material 10 is placed adjacent arear surface of the rear contact 42, and a backskin layer 28 is disposedadjacent a rear surface of the encapsulant material 10.

FIG. 7 is a cross-sectional view of a laminated glass or transparentpolymer assembly 70. A front support layer 62 formed of transparentmaterial is disposed adjacent a front surface 11 of the encapsulantmaterial 10 and a rear support layer 64 also formed of transparentmaterial is disposed adjacent a rear surface 13 to the encapsulantmaterial 10. The entire assembly 70 is then laminated to encapsulate thesupport layers 62, 64 with the encapsulant material 10.

The invention also features a UV stabilization additive package employedin the encapsulant material to prevent degradation. Photo-oxidation(oxidation caused by UV light) and thermal-oxidation (oxidation causedby heat) are two mechanism that cause degradation. By including astabilization additive package, the encapsulant material has the abilityto withstand. degradation for an extended period of time. When used insolar cell modules, the encapsulant material has the capability towithstand degradation for up to a thirty year service life. When used inlaminated glass or transparent polymer applications, the encapsulantmaterial can last even longer, since the encapsulant has no exposure tooxygen or water vapors except at the edges of the laminated structure.If the edges are well sealed, the likelihood of any photo-oxidationtaking place is very low.

The stabilization additive package must be appropriate for theapplications in which the encapsulant material is to be used and mustsatisfy solubility limitations of the two materials used as themetallocene polyethylene layer 12 and the acid copolymer layers 14, 16of the encapsulant material 10. A stabilization additive package has tobe soluble in both materials up to the level desired. Otherwise, aconcentration gradient and migration would occur. Metallocene polymersgenerally have lower solubility than acid copolymers, making theselection of stabilizers a non-trivial matter.

It has been determined that the stabilization additive package of theinvention need not contain an ultraviolet light absorber (UVA) nor aphenolic anti-oxidant (AO). Since in both solar cell module andlaminated glass applications, the glass filters a significant amount ofthe ultraviolet light from the sun, an ultraviolet light absorber is notneeded. Furthermore, some ultraviolet light absorbers are known toresult in yellowing themselves. It has also been determined that thestabilization system need not contain a phenolic AO, because theencapsulant material shows no significant loss of mechanical propertiesafter repeated extrusions and again, phenolic AOs are known to result inyellowing themselves.

Based on the foregoing considerations, the ultraviolet stabilizationadditive package of the invention comprises a combination of hinderedamine stabilizers. One hindered amine light stabilizer provides thermaloxidative and photo-oxidative stabilization and the second hinderedamine light stabilizer provides mainly photo-oxidative stabilization.

In one embodiment, the stabilization additive package includes 0.1-0.25%hindered amine with a high order of protection against thermal oxidationand photo-oxidation and 0.25-1.0% of hindered amine with a high order ofprotection mainly against photo-oxidation. Ideally, one hindered aminewould be preferred for both activities. However, a hindered amine thatcan perform both functions must also be sufficiently soluble inmetallocene polyethylene and acid copolymer used in the encapsulantmaterial, making this search difficult.

Examples of hindered amine stabilizers that provide thermal oxidativestabilization as well as photo-oxidative stabilization are1,3,5-Triazine-2,4,6-triamine,N,N′″-[1,2-ethanediylbis[[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidiny)amino]-1,3,5-triazine-2-yl]imino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-(Chimassorb119, CAS Reg. No. 106990-43-6);N,N′-bis(2,2,6,6-Tetramethyl-4-piperidinyl)-1,6-hexanediamine, polymerwith 2,4,6-trichloro-1,3,5-triazine and 2,4,4-trimethyl-1,2-pentamine(Chimassorb 944, ACS Reg. No. 70624-18-9); andN,N′-bis(2,2,6,6-Tetramethyl-4-piperidinyl)-1,6-hexanediamine polymerwith 2,4,6-trichloro-1,3,5-triazine and tetrahydro-1,4-oxazine (CyasorbUV 3346).

Examples of hindered amine stabilizers that provide photo-oxidativestabilization are dimethyl succinate polymer with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol (Tinuvin 622, CASReg. No. 65447-77-0); bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate(Tinuvin 770, ACS Reg. No. 52829-07-9); propandioic acid,[C4-(methoxyphenyl)-methylene]-,bis(1,2,2,6,6-pentamethyl-4-piperidinyl) ester, (CAS Registry No.94274-03-0, Sanduvor PR-31);Poly-methylpropyl-3-oxy-[4(2,2,6,6-tetramethyl)piperidinyl] siloxane(Uvasil 299HM); and3-Dodecyl-1-(2,2,6,6-tetramethyl-4-piperidinyl)-2,5-pyrrolidinedione(Cyasorb UV 3604).

In another embodiment, the hindered amine light stabilizers may begrafted onto a polymer structure. The Sanduvor PR-31 represents a newclass of hindered amine light stabilizers which graft onto a polymerstructure. Once a hindered amine light stabilizer is grafted onto apolymer, it remains in place as a stabilizer in the polymer.

EQUIVALENTS

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

We claim:
 1. An encapsulant material comprising: a first outer layer ofan acid copolymer of polyethylene; an inner layer of metallocenepolyethylene located next to a rear surface of the first outer layer; asecond outer layer of an acid copolymer of polyethylene located next toa rear surface of the layer of metallocene polyethylene, each of thefirst outer layer, the inner layer and the second outer layer comprisingan ultraviolet light stabilization additive package which comprises afirst hindered amine light stabilizer providing thermal oxidativestabilization and a second hindered amine light stabilizer providingphotooxidative stabilization.
 2. The encapsulant material of claim 1wherein the first outer layer of the acid copolymer of polyethylene andthe second outer layer of the acid copolymer of polyethylene are capableof adhering to an adjacent surface.
 3. The encapsulant material of claim1 wherein the inner layer of metallocene polyethylene comprisescomonomer of hexene.
 4. The encapsulant material of claim 1 wherein theinner layer of metallocene polyethylene comprises comonomer of butene.5. The encapsulant material of claim 1 wherein the metallocenepolyethylene is ethylene alpha-olefin comprising comonomer of octene. 6.The encapsulant material of claim 5 wherein the first outer layer of theacid copolymer of polyethylene and the second outer layer of the acidcopolymer of polyethylene, each comprises a copolymer of methacrylicacid and ethylene.
 7. The encapsulant material of claim 5 wherein thefirst outer layer of the acid copolymer of polyethylene and the secondouter layer of the acid copolymer of polyethylene, each comprises acopolymer of acrylic acid and ethylene.
 8. The encapsulant material ofclaim 1 wherein the first outer layer of the acid copolymer ofpolyethylene and the second outer layer of the acid copolymer ofpolyethylene each has free acid content of between 7 and 15% of anamount of the acid copolymer by weight.
 9. The encapsulant material ofclaim 1 wherein the inner layer of metallocene polyethylene, the firstand second outer layers of acid copolymer of polyethylene aresubstantially transparent.
 10. The encapsulant material of claim 1wherein the inner layer of metallocene polyethylene comprises twosublayers of metallocene polyethylene bonded together.
 11. Theencapsulant material of claim 1 wherein the first outer layer of theacid copolymer of polyethylene and the second outer layer of the acidcopolymer of polyethylene, each has a thickness in the range of0.001-0.004 inch.
 12. The encapsulant material of claim 1 wherein thefirst hindered amine light stabilizer forms 0.1-0.25% of the encapsulantmaterial by weight and the second hindred amine light stabilizer forms0.25-1.0% of the encapsulant material by weight.
 13. The encapsulantmaterial of claim 1 wherein the first hindered amine light stabilizer isa material selected from a group consisting of1,3,5-Triazine-2,4,6-triamine,N,N′″-[1,2-ethanediylbis[[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]amino]-3,1-propanediyl]]-bis[N′,N″-dibuty-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-;N,N′-bis(2,2,6,6-Tetramethyl-4-piperidinyl)-1,6-hexanediamine, polymerwith 2,4,6-trichloro-1,3,5-triazine and 2,4,4-trimethyl-1,2-pentamine;and N,N′-bis(2,2,6,6-Tetramethyl-4-piperidinyl)-1,6-hexandiamine,polymer with 2,4,6-trichloro-1,3,5-triazine and tetrahydro-1,4-oxazine;and the second hindered amine light stabilizer is a material selectedfrom a group consisting of Dimethyl succinate polymer with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol; and propandioicacid, [(4-methoxyphenyl)-methylene]-,bis(1,2,2,6,6-pentamethyl-4-piperidinyl) ester.
 14. A solar cell modulecomprising: at least one solar cell; a transparent encapsulant materialdisposed adjacent at least one surface of the solar cell, theencapsulant material comprising (1) a first outer layer of an acidcopolymer of polyethylene, (2) an inner layer of metallocenepolyethylene located next to a rear surface of the first outer layer,and (3) a second outer layer of an acid copolymer of polyethylenelocated next to a rear surface of the inner layer of metallocenepolyethylene; a front support layer formed of light transmittingmaterial disposed adjacent a front surface of the encapsulant material;and a backskin layer disposed adjacent a rear surface of the encapsulantmaterial.
 15. The solar cell module of claim 14 wherein the at least onesolar cell comprises a plurality of interconnected solar cells.
 16. Thesolar cell module of claim 14 wherein the encapsulant material comprisesa first encapsulant layer disposed adjacent a front surface of the solarcell and a second encapsulant layer disposed adjacent a rear surface ofthe solar cell.
 17. The solar cell module of claim 14 wherein the solarcell is formed of a film of semiconductor material and a transparentconductor, and the backskin is formed of a transparent conducting layer.18. The solar cell module of claim 17 wherein the film is formed ofcopper indium diselenide and the encapsulant material is disposed on afront surface of the transparent conducting layer.
 19. The solar cellmodule of claim 17 wherein the film is formed of amorphous silicon andthe encapsulant material is disposed on a rear surface of ametallization layer.
 20. The solar cell module of claim 17 wherein thefilm is formed of cadmium telluride and the encapsulant material isdisposed on a rear surface of a metallization layer.
 21. The solar cellmodule of claim 14 wherein the transparent encapsulant material furthercomprises an ultraviolet light stabilization additive package comprisinga first hindered amine light stabilizer providing thermal oxidativestabilization and a second hindered amine light stabilizer providingphoto-oxidative stabilization.
 22. The solar cell module of claim 21wherein the first hindered amine light stabilizer forms 0.1-0.25% of theencapsulant material by weight and the second hindered amine lightstabilizer forms 0.25-1.0% of the encapsulant material by weight. 23.The solar cell module of claim 21 wherein the first hindered amine lightstabilizer is a material selected from a group consisting of1,3,5-Triazine-2,4,6-triamine,N,N′″-[1,2-ethanediylbis[[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]amino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-;N,N′-bis(2,2,6,6-Tetramethyl-4-piperidinyl)-1,6-hexanediamine, polymerwith 2,4,6-trichloro-1,3,5-triazine and 2,4,4,trimethyl-1,2-pentamine;and N,N′-bis(2,2,6,6-Tetramethyl-4-piperidinyl)-1,6-hexanediaminepolymer with 2,4,6-trichloro-1,3,5-triazine and tetrahydro-1,4-oxazine;and the second hindered amine light stabilizer is a material selectedfrom a group consisting of Dimethyl succinate polymer with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol; and propandioicacid, [(4-methoxyphenyl)-methylene]-,bis(1,2,2,6,6-pentamethyl-4-piperidinyl) ester.
 24. A laminatedtransparent member comprising: a front support layer formed oftransparent material; a transparent encapsulant layer disposed adjacenta rear surface of the front support layer, the encapsulant layercomprising (1) a first outer layer of an acid copolymer of polyethylene,(2) an inner layer of metallocene polyethylene located next to a rearsurface of the first outer layer, and (3) a second outer layer of anacid copolymer of polyethylene located next to a rear surface of theinner layer of metallocene polyethylene, each of the first outer layer,the inner layer and the second outer layer comprising an ultravioletlight stabilization additive package which comprises a first hinderedamine light stabilizer providing thermal oxidative stabilization and asecond hindered amine light stabilizer providing photooxidativestabilization; and a rear support layer formed of transparent materialand disposed adjacent a rear surface of the encapsulant layer.
 25. Thelaminated transparent member of claim 24 wherein the front support layeris glass or plastic.
 26. The laminated transparent member of claim 24wherein the rear support layer is glass or plastic.
 27. The laminatedtransparent member of claim 24 wherein the first hindered amine lightstabilizer is a material selected from a group consisting of1,3,5-Triazine-2,4,6-triamine,N,N′″-[1,2-ethanediylbis[[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]amino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-;N,N′-bis(2,2,6,6-Tetramenthyl-4-piperidinyl)-1,6-hexanediamine, polymerwith 2,4,6-trichloro-1,3,5-triazine and 2,4,4,-trimethyl-1,2-pentamine;and N,N′-bis(2,2,6,6-Tetramenthyl-4-piperidinyl)-1,6-hexanediaminepolymer with 2,4,6-trichloro-1,3,5-triazine and tetrahydro-1,4-oxazine;and the second hindered amine light stabilizer is a material selectedfrom a group consisting of Dimethyl succinate polymer with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol; and propandioicacid, [(4-methoxyphenyl)-methylene]-,bis(1,2,2,6,6-pentamethyl-4-piperidinyl) ester.
 28. A method ofmanufacturing an encapsulant material comprising: providing a sheet ofmetallocene polyethylene comprising an ultraviolet light stabilizationadditive package; placing a first layer of an acid copolymer ofpolyethylene comprising an ultraviolet light stabilization additivepackage next to a front surface of the sheet of metallocenepolyethylene; and placing a second layer of an acid copolymer ofpolyethylene comprising an ultraviolet light stabilization additivepackage next to a rear surface of the sheet of metallocene polyethylene,wherein the ultraviolet light stabilization additive package comprises afirst hindered amine light stabilizer providing thermal oxidativestabilization and a second hindered amine light stabilizer providingphotooxidative stabilization.
 29. The method of claim 28 furthercomprising bonding the first layer of the acid copolymer of polyethyleneto the front surface of the sheet of metallocene polyethylene andbonding the second layer of the acid copolymer of polyethylene to therear surface of the sheet of metallocene polyethylene.
 30. The method ofclaim 28 wherein the sheet of metallocene polyethylene comprises a firstlayer of metallocene polyethylene and a second layer of metallocenepolyethylene.
 31. The method of claim 30 further comprising bonding thefirst layer of the acid copolymer of polyethylene and the first layer ofmetallocene polyethylene and bonding the second layer of the acidcopolymer of polyethylene and the second layer of metallocenepolyethylene.
 32. The method claim 30 further comprising bonding thefirst layer of metallocene polyethylene to the second layer ofmetallocene polyethylene.
 33. A method of manufacturing a solar cellmodule comprising: providing at least one solar cell; forming atransparent encapsulant material of: (1) a first layer of an acidcopolymer of polyethylene, (2) a layer of metallocene polyethylenelocated next to a rear surface of the first layer, and (3) a secondlayer of an acid copolymer of polyethylene located next to a rearsurface of the layer of metallocene polyethylene; placing theencapsulant material adjacent at least one surface of the solar cell;and positioning the solar cell and the encapsulant material between atransparent front support layer and a backskin layer.
 34. The method ofclaim 33 wherein forming a transparent encapsulant material comprisesadding an ultraviolet light stabilization additive package comprising afirst hindered amine light stabilizer providing thermal oxidativestabilization and a second hindered amine light stabilizer providingphoto-oxidative stabilization to the encapsulant material.
 35. A methodof manufacturing a laminated transparent member comprising: providingtwo transparent support layers; forming a transparent encapsulantcomprising: (1) a first layer of an acid copolymer of polyethylene, (2)a layer of metallocene polyethylene located next to a rear surface ofthe first layer, and (3) a second layer of an acid copolymer ofpolyethylene located next to a rear surface of the layer of metallocenepolyethylene, each of the first layer, the layer of metallocenepolyethylene and the second layer comprising an ultraviolet lightstabilization additive package which comprises a first hindered aminelight stabilizer providing thermal oxidative stabilization and a secondhindered amine light stabilizer providing photooxidative stabilization;placing the encapsulant layer in between the two support layers to forman assembly; and laminating the assembly to encapsulate the supportlayers with the encapsulant layer.